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.TH TM 3
.SH NAME
tm \- time conversion support
.SH SYNOPSIS
.L "#include <tm.h>"
.SH DESCRIPTION
The
.I tm
library supports conversion between
string date specifications,
.L time_t
clock values and
.L "struct tm"
values.
.L localtime()
and
.L gmtime()
(see
.IR ctime (3))
are used to determine local time zone information.
.PP
.L time_t
values are the number of seconds since the epoch,
.BR "Jan 1 00:00:00 GMT 1970" ,
with leap seconds omitted.
.PP
The global variable
.L "int tm_info.flags"
contains flags that allow all programs using the library
to be controlled in a consistent manner.
.L tm_info.flags
is initialized by the
.L tminit()
routine described below, and may be explicitly reset after
.L tminit()
is called.
The flags are:
.TP
.L TM_ADJUST
Set by
.L tminit()
if
.L localtime()
and
.L gmtime()
do not compensate for leap seconds.
.TP
.L TM_LEAP
.L time_t
values are interpreted as if they include leap seconds.
Set by
.L tminit()
if the
.L leap
option is set in the
.L TM_OPTIONS
environment variable.
.TP
.L TM_UTC
Times are relative to
.B UTC
(universal coordinated time, i.e.,
.BR GMT ).
Otherwise times are relative to the local time zone.
Set by
.L tminit()
if the time zone name matches one of
.L tm_info.format[43]
through
.L tm_info.format[46]
described below.
If the time zone name is not determined by
.L localtime()
then the environment variables
.L TZNAME
(as described in BSD 4.3) and
.L TZ
(as described in System V)
are checked, in order.
If this fails then the time zone name is constructed using
the local time zone offset.
.PP
The routines are:
.TP
.L "time_t tmdate(const char* date, char** end, time_t* clock)"
Parses the date specification
.L date
using the
.L tm_info.format
string table (described below)
and returns the equivalent
.L time_t
value.
If
.RL non- NULL ,
.L end
is set to the position of the first unrecognized character in
.LR date .
.L clock
is used to provide default values for omitted components in
.LR date .
If
.L clock
is
.L NULL
then the current time is used.
.TP
.L "struct tm* tmfix(struct tm* tp)"
Corrects any out of bounds fields in
.L tp
and returns
.L tp
as its value.
The corrections start with
.L tp->tm_sec
and propagate down to
.LR tp->tm_year .
For example, if
.L tp->tm_sec
were 61 then it would change to 1 and
.L tp->tm_min
would be incremented by 1, and so on.
.LR tp->tm_wday ,
.LR tp->tm_yday
and
.L tp->tm_isdst
are not changed as these can be computed from the other fields.
.TP
.L "char* tmfmt(char* buf, size_t len, const char* format, time_t* clock)"
Formats the date pointed to by
.L clock
into the buffer
.L buf
with size
.L len
bytes according to the format specification
.LR format .
If
.L format
is
.L NULL
or empty then the string
.L tm_info.format[40]
is used.
If
.L clock
is
.L NULL
then the current time is used.
A pointer to the end of
.L buf
(i.e., the terminating
.LR "'\e0'" )
is returned.
.RS
.PP
.L format
is in the style of
.IR printf (3),
where
.BI % field
causes the corresponding fixed size field to be placed in
.LR buf ,
zero padded if necessary, and \e\fIc\fP and \e\fInnn\fP
sequences are interpreted as in the C language.
Otherwise invalid
.BI % field
specifications and all other characters in
.L format
are copied into
.L buf
without change.
String field values are taken from the
.L tm_info.format
string table.
The
.I fields
are:
.TP
.PD 0
.B %
.B %
character.
.TP
.B a
Abbreviated weekday name.
.TP
.B A
Full weekday name.
.TP
.B b
Abbreviated month name.
.TP
.B c
.IR ctime (3)
style date without the trailing
.BR newline .
.TP
.B C
.IR date (1)
style date.
.TP
.B d
Day of month number.
.TP
.B D
Date as
.IR mm / dd / yy .
.TP
.B e
Blank padded day of month number.
.TP
.B E
Unpadded day of month number.
.TP
.B h
Abbreviated month name.
.TP
.B H
24-hour clock hour.
.TP
.B i
International
.IR date (1)
date that includes the time zone type name.
.TP
.B I
12-hour clock hour.
.TP
.B j
1-offset Julian date.
.TP
.B J
0-offset Julian date.
.TP
.B l
.IR ls (1)
.B \-l
date that lists recent dates with
.IR hh : mm
and distant dates with
.IR yyyy .
.TP
.B m
Month number.
.TP
.B M
Minutes.
.TP
.B n
.B newline
character.
.TP
.B p
Meridian (e.g.,
.B AM
or
.BR PM ).
.TP
.B r
12-hour time as
.IR hh : mm : ss
.IR meridian .
.TP
.B R
24-hour time as
.IR hh : mm .
.TP
.B S
Seconds.
.TP
.B t
.B tab
character.
.TP
.B T
24-hour time as
.IR hh : mm : ss .
.TP
.B U
Week number with Sunday as the first day.
.TP
.B w
Weekday number.
.TP
.B W
Week number with Monday as the first day.
.TP
.B x
Local date style, using
.LR tm_info.format[39] ,
that includes the month, day and year.
.TP
.B X
Local time style, using
.LR tm_info.format[38] ,
that includes the hours and minutes.
.TP
.B y
2-digit year.
.TP
.B Y
4-digit year.
.TP
.B z
Time zone type name.
.TP
.B Z
Time zone name.
.TP
.BI + flag
.TP
.BI \- flag
Temporarily (until
.L tmform()
returns) sets (+) or clears (\-) the
.L tm_info.flags
flags specified by
.IR flag :
.RS
.TP
.B l
.L TM_LEAP
.TP
.B u
.L TM_UTC
.RE
.TP
.B #
Number of seconds since the epoch.
.PD
.RE
.TP
.L "void tminit(Tm_zone_t* zone)"
Implicitly called by the other
.I tm
library routines to initialize global data, including the
.L tm_info.format
table and the
.L tm_info.flags
global flags.
Global data should only be modified after an explicit call to
.LR tminit .
If
.L "zone != 0"
then it specifies a time zone other that the local time zone.
.TP
.L "void tmset(Tm_zone_t* zone);"
.L tmset
sets the reference timezoe to
.LR zone .
.L tm_info.local 
points to the local timezone and
.L tm_info.zone
points to the current reference timezone.
.TP
.L "time_t tmleap(time_t* clock)"
Returns a
.L time_t
value for the time pointed to by
.L clock
with leap seconds adjusted for external
routines that do not handle leap seconds.
If
.L clock
is
.L NULL
then the current time is used.
Adjustments are only done if the
.L TM_ADJUST
flag is set in
.LR tm_info.flags .
.TP
.L "struct tm* tmmake(time_t* clock)"
Returns a pointer to the
.L tm
struct corresponding to the time pointed to by
.LR clock .
If
.L clock
is
.L NULL
then the current time is used.
.TP
.L "time_t tmtime(struct tm* tp, int west)"
Returns the
.L time_t
value corresponding to
.LR tp .
If
.L west
is
.L TM_LOCALZONE
then
.L tm
is relative to the local time zone,
otherwise
.L west
is the number of minutes west of
.B UTC
with daylight savings time taken into account.
.LR tp->tm_wday ,
.LR tp->tm_yday
and
.L tp->tm_isdst
are ignored in the conversion.
.PP
The library routines use a table of date strings pointed to by
.LR "char** tm_info.format" .
The indices in
.L tm_info.format
are fixed by category.
.L tm_info.format
may be changed to point to other tables
according to local language and date conventions.
The contents by index (showing the USA English values) are:
.RS
.TP
.PD 0
.B 0-11
3-character abbreviated month names.
.TP
.B 12-23
Full month names.
.TP
.B 24-30
3-character abbreviated weekday names.
.TP
.B 31-37
Full weekday names.
.TP
.B 38
.L tmform()
local time format used by the
.B %X
field.
.TP
.B 39
.L tmform()
local date format used by the
.B %x
field.
.TP
.B 40
.L tmform()
format used if the
.L format
argument is
.L NULL
or empty.
.TP
.B 41-42
Meridian names: AM, PM.
.TP
.B 43-46
.B UTC
time zone names: GMT, UTC, UCT, CUT.
.TP
.B 47-50
Daylight savings time suffix names: DST.
.TP
.B 51-54
Suffixes to be ignored when matching strings in
.LR tmform() .
.TP
.B 55-61
Time part names: second, hour, minute, day, week, month, year.
.TP
.B 62-65
Hours of the day names: midnight, morning, noon, evening.
.TP
.B 66-68
Relative day names: yesterday, today, tomorrow.
.TP
.B 69-71
Past relative time references: last, ago, past.
.TP
.B 72-75
Current relative time references: this, now, current.
.TP
.B 75-77
Future relative time references: next, hence, coming.
.TP
.B 78-80
Exact relative time references: exactly.
.TP
.B 81-85
Noise words to be ignored: at, in, on.
.PD
.RE
.PP
Low level support functions and data are described in
.LR <tm.h> .
.SH EXAMPLES
.EX
#include <tm.h>
main() {
    int       i;
    time_t    t;
    char      buf[128];
    struct {
        char* date;
        char* format;
    }         x[] = {
        "now",                 "%i",
        "2 months ago",        "%C",
        "this Wednesday noon", "%x %I:%M %p",
        "last December 25",    "%A",
        0,                     0
    };
    for (i = 0; x[i].date; i++) {
        t = tmdate(x[i].date, (char*)0, (time_t*)0);
        (void)tmform(buf, x[i].format, &t);
        puts(buf);
    }
}
.EE
produces
.EX
Fri Sep 30 12:10:14 USA EDT 1988
Fri Jul  1 00:00:00 EDT 1988
10/05/88 12:00 PM
Friday
.EE
.SH "SEE ALSO"
date(1), time(2), ctime(3)
.SH BUGS
.L "struct tm"
values may get clobbered by the
.I tm
library routines as the
.IR ctime (3)
routines typically return pointers to a single static
.L "struct tm"
area.
.L tmdate()
uses an internal international time zone name table that will
probably always be incomplete.
